A solar cell is a photovoltaic (PV) device having one or more p-n junctions. Each junction comprises two different regions within a semiconductor material where one side is denoted as the p-type region and the other as the n-type region. When light, specifically solar light, is incident upon these regions, the light is directly converted to electricity through the PV effect. In the PV effect, light-generated carriers (electrons) are collected, and can either be conducted away as an electrical current or remain in the device to give rise to a voltage, termed a photovoltage.
The solar cell may operate with sunlight of normal intensity, or the sunlight may be concentrated onto the solar cell using a mirror or a lens. Concentrator solar cells having multiple stacked junctions produce the highest conversion efficiencies of light to electricity. Concentrator solar cell systems with concentration ratios ranging from 100 to 500 suns are contemplated, and even higher concentration ratios may be used in the future. The temperature of such concentrator solar cells may reach 300° C. or higher during operation, depending upon the environment for which the solar cell was designed.
In the work leading to the present invention, testing of concentrator solar cells operating over extended periods of time at elevated temperatures has led to premature failures that are not typically observed in conventional non-concentrator solar cells. If they are not built properly, the concentrator solar cells may have a higher risk of failure than non-concentrator solar cells. The premature failure is of particular concern because it is expected that the concentrator solar cells will find use to power spacecraft for earth-orbiting and deep-space missions, where the concentrator solar cells cannot be readily replaced in the event of a failure.
There is therefore a need for an improved approach to the structure of solar cells, particularly solar cells that are to be used in concentrator applications that require high-temperature operation. The present invention fulfills this need, and further provides related advantages.